In bipolar disorder, do moods fluctuate over the course of weeks, or over the course of hours in a day?

Both: Typical mood swing or change happens over days or weeks going from mania to depression. However during mania or depressive phase irritability is common as well as mood lability.

Bipolar Disorder: Bipolar disorder moods can fluctuate at all different frequencies. More often this occurs over the course of weeks/months. But there are people with very rapid cycling bipolar disorder, whose moods can fluctuate over the course of hours. These fluctuations can also be misdiagnosed; the differential includes ptsd and also certain personality disorders.

Moods: Daily fluctuations are more associated with rapid cycling, whether hormonal or bipolar type 2 (cyclothymia).